1. Field of the Invention
The present invention is related to very large scale integrated circuit chips and more specifically to a method and apparatus for maintaining functional operation when chip temperatures exceed operating temperature specifications.
2. Prior Art
A notebook computer is a small, lightweight, portable, battery-powered, lap-top personal computer (PC) that uses a thin, lightweight, display screen such as a liquid crystal display (LCD). Notebook PCs typically run several hours on rechargeable batteries, weigh 4-7 pounds, fold up, and can be carried like a briefcase. Because of their small size and portability these small devices are often times exposed to environments where the temperature range for which the microprocessor chips were designed is greatly exceeded. This could lead to intermittent operation of the device and a shortened lifetime of the integrated circuit chips that make up the device's logical circuits.
Phase-locked loop (PLL) clocks are placed on integrated circuit chips to minimize clock delay skew between a board-level system clock and latches fabricated on the chip. The delay skew is created by the number of buffering levels needed on the chip to distribute the clock signal to all of the latches on the chip. PLL's can also change the frequency of the board level system clock so that the chip clock frequency is higher or lower than the board level system clock. It is well known that logical circuits consume power in proportion to the frequency at which they operate. The higher the operational frequency, the higher the power dissipation. By controlling the clock frequency to the logic, one can control the power dissipation.
It is therefore an object of this invention to provide a method and means for controlling the temperature of a very large scale integrated (VLSI) circuit chip by controlling phase locked loop (PLL) clock circuitry existing on the chip.